Pulse oximetry is a non-invasive technique which is useful for measuring certain vascular conditions. In pulse oximetry, light is passed through a portion of a patient's body, which contains arterial blood flow. An optical sensor detects the light which has passed through the body, and the variations in the detected light at various wavelengths are then used to determine the arterial oxygen saturation and/or pulse rates. Oxygen saturation may be calculated using the absorption equation known as Beer's Law.
The accurate measurement of oxygen saturation is dependent upon several factors which affect the supply of blood in the body part that is being used for the measurement. For example, blood flow can be affected by vasoconstriction. One cause of vasoconstriction can be the pressure exerted by the sensor on the finger or other body part of the patient. Many currently available pulse oximetry sensors have a hard shell which is maintained on a finger by the action of a spring. Since excessive pressure on the finger can dampen or eliminate the pulsations in the finger's blood supply, these springs are intentionally made very soft. The result is that such spring-held sensors are not completely satisfactory because they may fall off the finger.
A sensor that does not employ a spring is described in the Thomas et al. U.S. Pat. No. 5,170,786. The pressure exerted by that sensor is determined by the tightness with which the sensor is wrapped about a finger. However, that sensor is not readily preassembled and it could be relatively expensive to make.
It would be desirable to have a sensor which can be preassembled, which does not employ a spring and which is inexpensive enough to be disposed of after a single use.